The present invention refers to a method and an apparatus for eliminating inclination of a wheel-block bogie (or undercarriage) which is provided with several individual wheels.
Rail vehicles consist of a car body and an undercarriage. The undercarriage has two purposes: It assumes the guidance of the vehicle in the track of the rails and must protect the car body from blows.
The tracking is ideal when the vehicle precisely follows the center of the rails. The faster deviations from the axis of the rails are corrected, the closer the tracking behavior of the undercarriage comes to ideal tracking.
The tracking behavior can be judged rapidly on the basis of merely two parameters, including:
the correction of transverse offset, and PA1 the correction of a tilt in the rails.
Forces are necessary for the transverse shifting and a yawing moment is required for correction of the inclination. The latter, in its turn, requires forces which supply the desired moment with a lever arm around a suitable pivot point or as a force couple.
Forces which can be used for the guidance are produced in the wheel/rail contact surface. Depending on the physical effect, two fundamentally different types of forces can be distinguished.
Frictional (non-positive) forces are present when the wheel slides transversely or longitudinally relative to the rail at the wheel contact point. The product of relative speed times frictional force is a frictional power loss. It makes itself noticeable as resistance to tracking and is converted in the wheel/rail contact into heat and wear of the wheel and the rail. The wheel noise is also closely related thereto.
In the article "Askpekte zur Spurfuhrung" (Aspects of Tracking), published in the journal ZEV-Glas. Ann. 114 (1990), No. 1/2, pages 24 to 29, various tracking principles are set forth and examined with regard to tracking behavior. The "wheel block" tracking principle is discussed in this article. In a wheel block, two individual wheels are used which are arranged one behind the other rather than alongside each other. The individual wheels arranged behind one another prove to be practically ideal for the correction of inclination. Frictional cross sections of equal size act on both wheels of the inclined wheel block due to the same angle of inclination .delta.. With reference to the pivot point, they compensate for the yawing moments produced thereby. From this point of view the wheel block is always in indifferent equilibrium. From any given position of the phase diagram of the wheel block, the transverse deflections and inclination are very rapidly reduced to values of about zero. The wheel block counteracts both the transverse offset and inclinations with profile side forces and is thus free of wear. The wheel block tracking principle would come very close to being ideal if there were no frictional longitudinal forces such as that present in the case of driven wheels.
A rail vehicle is described in European Patent Document No. EP 0 374 290 A1 which has, on both sides, along the longitudinal axis of the vehicle a predetermined number of individual wheels which are swingable by steering. A steering of each individual wheel which is free of tracking errors in all regions of curves is obtained in the manner that a rail path measuring device is provided which measures the deviation of an axle of the vehicle from the path of the rail and which, depending on measured deviations, produces a steering signal for each individual wheel independently, in each case, of the other wheel. Thus, in any curve each individual wheel is always correctly steered so that tracking errors can no longer occur.
Upon travel around curves, the wheel planes should ideally be tangential to the rail. Nevertheless, unconstrained travel of the wheels is assured only if the rolling radii of the wheels are relatively the same as the arc lengths of the two rails. This permits a transverse offset. The necessary difference in the rolling diameter due to the conicity of the wheel profiles of the two wheels results in the known travel condition of the wheel set. If, as a result of the rail guidance, the necessary difference in the rolling radii is greater than the possible difference based on the wheel profile, the wheels can no longer travel in unconstrained fashion. In other words, the wheel which is on the outside of the curve therefore turns too slowly and the wheel on the inside of the curve turns too fast. With respect to the vertical axis, a yawing moment is produced by the different frictional longitudinal forces, this moment turning the undercarriage, also known as the bogie, out of the arc. Running onto the wheel flange takes place whenever the bogie is inclined and therefore is no longer parallel to the rail or no longer travels tangentially to the rail along curves. The opposing moment can be applied only by the frictional transverse forces or by running onto the wheel flange, with corresponding wear.